We intend to investigate the genomic organization of a variety of genes expressed in the human red cell. This project will utilize immunologic analysis of in vitro translation products stimulated by specific reticulocyte messenger RNA to identify corresponding cDNA clones. Such clones will be used as probes to identify the corresponding genes in a genomic recombinant DNA library. Each of the genomic clones will be analyzed for clues to the genomic elements responsible for coordinate gene expression during red cell differentiation. A second line of inquiry involves analysis of the DNA sequence organization of individual human chromosomes. We will enlarge our bank of X chromosome sequences by screening a recombinant DNA library constructed with DNA from a mouse x human somatic hybrid cell and in which the only human chromosome is the X. These clones will be used to investigate the evolution of the X chromosome DNA and to probe for DNA modification as the mechanism for X chromosome inactivation. DNA sequences specific for the human Y chromosome will be used to screen a genomic recombinant DNA library for additional Y chromosome sequences.